Improve the heat dissipation of LED packages

Improve the heat dissipation of LED packaging

The heat dissipation method of LEDs has been improved to improve the efficiency of heat conduction from the LED substrate to the heat sink. The common point is that the substrate uses an aluminum alloy plate and a metal base plate with an insulating layer between the wiring pattern. The measures taken to facilitate heat conduction from the LED chip to the base plate mounting area are not much different.

In the future, in order to realize LED bulbs with brightness equivalent to that of 100W incandescent bulbs , different measures to improve heat dissipation will be needed. New LED packages are one of these measures.

Nippon Tungsten has developed an LED package consisting of a silver-plated copper lead frame and a ceramic housing (Figure 15). This package will be used as a chip substrate supplier without LED chips installed.

Figure 15: The silver-plated copper lead frame of the LED package provided by Japan Tungsten is fixed to the lower-priced ceramic housing. Heat is mainly conducted to the heat sink through the lead frame.

In the past, there were products that used high thermal conductivity aluminum nitride as the LED package shell. The heat of the LED can be transferred to the package base through the shell. Although this shell can achieve high- power LED packaging due to its superior thermal conductivity and heat resistance compared to resin shells, it is expensive.

In contrast, Japan Tungsten's chip package base uses a copper lead frame as a heat conduction path instead of an LED package shell. The shell uses cheap ceramics with poor thermal conductivity but excellent heat resistance. This reduces the cost to half of the original ceramic LED package.

Although the structure of this package is very simple, copper has a low melting point and is difficult to combine with ceramics. To this end, the company independently developed ceramics that can be fired at a temperature lower than the melting point of copper and have strong bonding with copper. By improving the temperature control and fixing method during firing, it successfully developed a high-precision chip base with a spacing of less than 70μm between electrodes (between the tops of the lead frame) (Figure 16). Samples are now available.

Figure 16: Japan Tungsten's LED package prototype and thermal conductivity analysis results The company has developed a ceramic that can be fired at a temperature lower than the melting point of copper and has a high ability to bond with copper. The prototype can be installed with 10 LED chips, and the thermal conductivity is good. The temperature difference between the LED chip and the lead frame is about 2°C. In the thermal conductivity analysis, the closer to red, the higher the temperature.

Denki Kagaku Kogyo's "Electrified AGSP Base Plate" is also one of the means to improve the heat dissipation of LED packages. The company used the technology developed by Yamato Kogyo (Headquarters: Okaya City, Nagano Prefecture) to create a base plate with copper pillars of any shape running through any position. If the base plate is used as part of the LED package shell, the heat can be transferred to the heat sink through the contact between the copper pillars and the LED chip. Although there are still issues that need to be resolved in terms of cost, the adoption of new packages is fully expected to expand in the future.